Paperboard cartons or carriers are used to package a variety of different types of articles, including beverage containers. When used to package beverage cans some carriers are designed to receive the cans so that the ends of the cans are adjacent the side panels of the carrier while others are designed so that the cans are positioned with their tops adjacent the top panel and their bottoms adjacent the bottom panel. In either arrangement the cans are normally tightly held in place inside the carrier, with the ends of the cans engaging the adjacent panels. A common example is a carrier designed to hold twelve cans, with the can ends contacting the side panels of the carrier so tightly that the impressions of the can ends can be seen in the outer surface of the side panels.
It is of course necessary to tightly package the cans in order to prevent them from breaking free of the carrier during handling. It will be appreciated that in the course of shipping and unloading the carriers, they may be subjected to impact loads caused by being dropped or roughly piled on top of one another. Because the carriers are designed to withstand this type of treatment they normally do not fail as a result. Sharp blows on the can ends through the carrier panels can, however, produce an adverse effect on the cans themselves.
The beverage cans packaged in paperboard carriers typically are aluminum cans formed with a generally flat top recessed from a relatively narrow top rim. The rim is quite rigid and capable of receiving hard blows on its edge without deforming. The bottoms are typically of concave shape recessed from a somewhat wider bottom rim which does not have the edge strength of the top rim. The bottom rim instead is more of an integral contour of the can bottom and, as such, can more readily be deformed or driven up into the body of the can.
When such a carrier is dropped or harshly stacked the bottom rims of the cans adjacent the carrier panel receiving the blow are in danger of being flattened in the area of the impact or pushed up into the interior of the can. When the bottom rim is pushed up into the can the resulting reduction in can volume causes the liquid inside the can to exert sufficient additional pressure on the bottom to bow the bottom out from its original concave configuration to a convex shape, thereby relieving the pressure. This action is known as "doming". While the doming phenomenon allows the can to retain its liquid without splitting or otherwise failing, when a consumer uses the can the curved dome-shaped bottom cannot hold the can in steady condition on a table or other support surface. Even if the impact to the bottom rim is not enough to cause severe doming, the rim will often be flattened where the impact occurred to the extent that the can is unsteady when placed upright on a support surface.
It would be highly desirable to be able to package beverage cans in a manner which prevents damage to the can bottoms but does not require costly new packages or major modification to packaging machines currently in use.